EP-A-0735747 discloses a method of noise measurement in conjunction with a block-matching motion estimation algorithm, the principle of which is to derive a noise level from the minimum of accumulated absolute pixel difference values, leading to a displaced field or frame differences (DFD) value, the accumulation taking place over predetermined pixel blocks.
A paper by Q. Zhang and R. Ward, entitled "Automatic assessment of signal-to-thermal noise ratio of television images", Vol. 41, No. 1, IEEE Transactions on Consumer Electronics (February 1995), discloses a method for measuring the noise level from the TV pictures as such. This method is based on the application of a two-dimensional highpass filter on the images in order to remove the majority of the (non-noisy) image content. Thereafter the smoothest regions of the picture, i.e. those having minimum energy with respect to brightness variations, are selected and the noise power is estimated from their remaining average power.
That paper says that in digital image processing the customary procedure to estimate the level of thermal noise in the image is to analyse "smooth regions, i.e. regions containing constant luminance (grey levels)".